204 C. M. CHILD 



121). Thus far, this condition has been observed only in ether. 

 In alcohol, on the other hand, some development of new tissue 

 occurs in any concentration which does not kill. 



The morphological effect of chloretone is very similar to that 

 of alcohol but appears with much lower concentrations (alcohol 

 1-1.5 per cent; chloretone 0.02-0.025 per cent). 



As already mentioned above (p. 188) a much greater degree of 

 maceration and apparent solution of the tissues occurs in alcohol, 

 ether, chloretone and benzamid than in KCN; this may be due 

 to the different effects of these substances on the lipoids. 



The effects of low temperature are in general similar to those 

 produced by the substances mentioned, but in low temperature 

 the growth of new tissue is merely retarded, not inhibited. The 

 relation between the formation of new tissue at the cut surface 

 and the redifferentiation back of the cut is much the same as under 

 the usual conditions. In this respect low temperature differs in 

 its action from all the substances used. 



Thus far I have not been able to discover any features strictly 

 characteristic of the animals which develop in water containing 

 an excess of their own metabolic products. Conditions of this 

 sort which produce marked morphological effects usually produce 

 also a high mortality as is the case with alcohol and the morpho- 

 logical effects resemble those of alcohol. 



More attention directed to this point will doubtless bring to 

 light other morphological or physiological effects characteristic 

 of the different substances. At present, however, there seems to 

 be no ground for believing that any of these features which are 

 more or less characteristic of one or the other substance are specific 

 chemical effects. Some of them may conceivably be such, but 

 it is much more probable that they are the result of incidental 

 physical factors, e.g., osmotic conditions, coefficient of distribu- 

 tion, etc. In general the morphological effects of these substances 

 and conditions are due primarily to differences in the rate of 

 reaction in different developing organs and regions. 



In more highly differentiated animals than Planaria, where the 

 difference in constitution in different organs is much greater than 

 here it should be possible to produce morphological effects with 



